1. Field of the Invention
The present invention relates to a hardness testing instrument and a calibration method for a hardness testing instrument.
2. Description of Related Art
There has been a hardness testing instrument well-known which measures a hardness of a specimen by forming an indentation with an indenter on a surface of the specimen (for example, Japanese Patent No. 3170256).
When force calibration is performed on the conventional hardness testing instrument, it is performed at one intermediate position of a mechanical stroke, and maintenance and management of quality is done by calibration at this one position.
In recent years, as improvement of traceability system is promoted, need is rising for performing calibration of force for three standards in the stroke of the hardness testing instrument, and quality management at a higher level is demanded.
However, there is a problem of when force calibration is performed on the conventional hardness testing instrument, in order to perform calibration of force (load) for the three standards, fine adjustment such as position adjustment of specimen table with respect to each standard needs to be performed, and complicated operation is necessary.
Specifically, in order to set a load cell for calibration at the target standard, after performing measurement of indentation depth using a reference block and measurement of distortion amount of the load cell, the moving amount of the specimen table needed to be determined by hand calculation. Also, measurement of the reference block needs to be performed each time due to individual difference according to model such as machine casing distortion of the hardness testing instrument.
In a conventional hardness testing instrument which performs a sequence of applying test force (load) at a set position of a specimen, after the test force is unloaded, the preliminary test force is still loaded, therefore the lifting and lowering device needs to be operated to lower the specimen table and the test force needs to be released. Therefore, when data is obtained a plurality of times, alignment of the height position of the load cell needs to be performed again after the release of the test force.